Apex domains cannot have CNAME records.
Question and response
Question
dig static.optonline.net. NS
Answer
static.optonline.net. 5 NS authns1.cvnet.com.
static.optonline.net. 5 NS authns1.cv.net.
Authority
The response has no authority records.
Additional
authns1.cv.net. 4 A 167.206.12.12
authns1.cvnet.com. 4 A 167.206.13.20
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0